Re: [netmod] WG Last Call: draft-ietf-netmod-acl-model-14

Robert Wilton <rwilton@cisco.com> Thu, 02 November 2017 11:24 UTC

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To: Mahesh Jethanandani <mjethanandani@gmail.com>, Kristian Larsson <kristian@spritelink.net>, "netmod@ietf.org" <netmod@ietf.org>
References: <51DBEB86-2482-4D37-9F97-5EEE76B38285@juniper.net> <20171031102523.GB25608@spritelink.se> <CDEF081E-C5AA-459B-8DBB-770D5065FD26@gmail.com> <20171101112249.wmq4ggx2ixgn4kqo@elstar.local> <A55809F6-23FA-404D-BC0F-74AF11F508BF@gmail.com> <20171102074318.GC12688@spritelink.se> <6359CD50-0F0D-4315-A58B-1D4CF0583475@gmail.com>
From: Robert Wilton <rwilton@cisco.com>
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Date: Thu, 2 Nov 2017 11:24:40 +0000
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Subject: Re: [netmod] WG Last Call: draft-ietf-netmod-acl-model-14
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Hi Mahesh,

I also think that the model would be cleaner if you don't have separate 
containers for each "type of ACL".  In particular, I think that the 
model is easier for clients, and perhaps easier to implement, if a given 
ACE field is always on the same path rather that being on a different 
path based on ACL type.  I've suggested a minor change to the model that 
may retain the same benefits, but keep consistent paths for the ACE fields.

Hence, would the following help improve the model?

1) Move the L2, IPv4, IPv6 match fields under their own containers, as 
Juergen/Kristian have suggested.
2) Under each of those containers remove the "if-feature", and change 
the "must" statement to a "when statement".
3) Add if-feature statements under the acl-type identity definitions, 
allowing a device to control what acl-types mixes they support.

E.g.

   // ACL features defined as below.

   // ACL type identities updated to:
   identity ipv4-acl {
     base acl:acl-base;
     if-feature "ipv4-acl";
   }
   identity ipv6-acl {
     base acl:acl-base;
     if-feature "ipv6-acl";
  }
   identity eth-acl {
     base acl:acl-base;
     if-feature "l2-acl";
  }
   identity mixed-l2-l3-ipv4-acl {
     base "acl:ipv4-acl";
     base "acl:eth-acl";
     if-feature "mixed-ipv4-acl";
  }
   identity mixed-l2-l3-ipv6-acl {
     base "acl:ipv6-acl";
     base "acl:eth-acl";
     if-feature "mixed-ipv6-acl";
  }

...

...
       leaf acl-type {
         type acl-type;
       }
       container aces {
         list ace {
           key "rule-name";
           ordered-by user;
           leaf rule-name ...

           container matches {
             container l2 {
               when "derived-from(../../../../acl-type, 'acl:eth-acl')";
               uses packet-fields:acl-eth-header-fields;
               description
                 "Rule set for L2 ACL.";
             }
             container ipv4 {
               when "derived-from(../../../../acl-type, acl:ipv4-acl')";
               uses packet-fields:acl-ip-header-fields;
                     uses packet-fields:acl-ipv4-header-fields;
               description
                 "Rule set that supports IPv4 headers.";
             }
             container ipv6 {
               ...
             }


Thanks,
Rob


On 02/11/2017 08:50, Mahesh Jethanandani wrote:
> Kristian,
>
> I hear you. What I am providing is the rational for the current design.
>
> I would like to hear from others in the WG. We have been reviewing this draft for the last couple of years, and we are now at the tail end of the LC. I would really like to see this draft move forward, particularly since it is not broken.
>
> Thanks.
>
>> On Nov 2, 2017, at 2:13 PM, Kristian Larsson <kristian@spritelink.net> wrote:
>>
>>> On Thu, Nov 02, 2017 at 06:13:04AM +0630, Mahesh Jethanandani wrote:
>>>     On Nov 1, 2017, at 5:52 PM, Juergen Schoenwaelder <
>>>     j.schoenwaelder@jacobs-university.de> wrote:
>>>
>>>     Mahesh,
>>>
>>>     I think the question is why we need to have different match containers
>>>     for each possible feature set combination instead of having a single
>>>     match container with groups of leafs in it marked as features. This
>>>     would seem to cut down the size of the module and the tree diagram
>>>     significantly. I think this will also make clients simpler sicne they
>>>     do not have to select a certain container based on the feature set
>>>     announced.
>>>
>>>
>>> The current design of match containers was chosen to allow platforms to select
>>> one container that matched what the hardware supported from a l2, l3 and ipv
>>> {4,6} perspective.
>> Sure, but you are conflating the structure of the model with the
>> feature-wraps. Without changing the features of the model, we can
>> structure it in a different way where there is not a 1:1 mapping
>> between features and containers under the matches container.
>>
>>
>>> I would argue that even though the overall diagram is bigger
>>> with this design, once the platform selects the container of choice, the tree
>>> and the configuration itself would be a little simpler/smaller.
>> I am arguing the opposite. It's really awkward to place the same
>> type of data, like IPv4 match conditions, under different paths
>> based on a feature.
>>
>> If the system model had done the same we would have:
>> /system
>> /system-with-ntp
>> /system-with-ntp-and-radius
>>
>> How do you augment in new leaves? While you are using groupings
>> which allows for a reuse of data across all these containers,
>> someone who is augmenting can't, since you can't augment a
>> container, only where it is used. Someone wishing to add a leaf
>> to the model needs to augment in three different locations to
>> support a new match condition for IPv4 (let's say some meta-data
>> attribute).
>>
>>
>>> Take the case where the desired selection is l2,-l3, ipv4 and ipv6. The current
>>> tree looks like this:
>>>
>>>
>>>         |        |  +--rw l2-l3-ipv4-ipv6-acl {l2-l3-ipv4-ipv6-acl}?
>>>         |        |  |  +--rw destination-mac-address?        yang:mac-address
>>>         |        |  |  +--rw destination-mac-address-mask?   yang:mac-address
>>>         |        |  |  +--rw source-mac-address?             yang:mac-address
>>>         |        |  |  +--rw source-mac-address-mask?        yang:mac-address
>>>         |        |  |  +--rw ethertype?                      eth:ethertype
>>>         |        |  |  +--rw dscp?                           inet:dscp
>>>         |        |  |  +--rw ecn?                            uint8
>>>         |        |  |  +--rw length?                         uint16
>>>         |        |  |  +--rw ttl?                            uint8
>>>         |        |  |  +--rw protocol?                       uint8
>>>         |        |  |  +--rw source-port-range!
>>>         |        |  |  |  +--rw lower-port    inet:port-number
>>>         |        |  |  |  +--rw upper-port?   inet:port-number
>>>         |        |  |  |  +--rw operation?    operator
>>>         |        |  |  +--rw destination-port-range!
>>>         |        |  |  |  +--rw lower-port    inet:port-number
>>>         |        |  |  |  +--rw upper-port?   inet:port-number
>>>         |        |  |  |  +--rw operations?   operator
>>>         |        |  |  +--rw ihl?                            uint8
>>>         |        |  |  +--rw flags?                          bits
>>>         |        |  |  +--rw offset?                         uint16
>>>         |        |  |  +--rw identification?                 uint16
>>>         |        |  |  +--rw destination-ipv4-network?       inet:ipv4-prefix
>>>         |        |  |  +--rw source-ipv4-network?            inet:ipv4-prefix
>>>         |        |  |  +--rw next-header?                    uint8
>>>         |        |  |  +--rw destination-ipv6-network?       inet:ipv6-prefix
>>>         |        |  |  +--rw source-ipv6-network?            inet:ipv6-prefix
>>>
>>>         |        |  |  +--rw flow-label?
>>>         |        |  |          inet:ipv6-flow-label
>>>
>>>
>>>
>>> whereas, if the design went with one match container with each group of leafs
>>> in their own container (to support the if-feature statement for that
>>> container), the tree would look like this:
>>>
>>>
>>>         |        |  +--rw l2-acl {l2-acl}?
>>>         |        |  |  +--rw destination-mac-address?        yang:mac-address
>>>         |        |  |  +--rw destination-mac-address-mask?   yang:mac-address
>>>         |        |  |  +--rw source-mac-address?             yang:mac-address
>>>         |        |  |  +--rw source-mac-address-mask?        yang:mac-address
>>>         |        |  |  +--rw ethertype?                      eth:ethertype
>>>
>>>         |        |  +--rw ipv4-acl {ipv4-acl}?
>>>         |        |  |  +--rw dscp?                       inet:dscp
>>>         |        |  |  +--rw ecn?                        uint8
>>>         |        |  |  +--rw length?                     uint16
>>>         |        |  |  +--rw ttl?                        uint8
>>>         |        |  |  +--rw protocol?                   uint8
>>>         |        |  |  +--rw source-port-range!
>>>         |        |  |  |  +--rw lower-port    inet:port-number
>>>         |        |  |  |  +--rw upper-port?   inet:port-number
>>>         |        |  |  |  +--rw operation?    operator
>>>         |        |  |  +--rw destination-port-range!
>>>         |        |  |  |  +--rw lower-port    inet:port-number
>>>         |        |  |  |  +--rw upper-port?   inet:port-number
>>>         |        |  |  |  +--rw operations?   operator
>>>         |        |  |  +--rw ihl?                        uint8
>>>         |        |  |  +--rw flags?                      bits
>>>         |        |  |  +--rw offset?                     uint16
>>>         |        |  |  +--rw identification?             uint16
>>>         |        |  |  +--rw destination-ipv4-network?   inet:ipv4-prefix
>>>         |        |  |  +--rw source-ipv4-network?        inet:ipv4-prefix
>>>         |        |  +--rw ipv6-acl {ipv6-acl}?
>>>         |        |  |  +--rw dscp?                       inet:dscp
>>>         |        |  |  +--rw ecn?                        uint8
>>>         |        |  |  +--rw length?                     uint16
>>>         |        |  |  +--rw ttl?                        uint8
>>>         |        |  |  +--rw protocol?                   uint8
>>>         |        |  |  +--rw source-port-range!
>>>         |        |  |  |  +--rw lower-port    inet:port-number
>>>         |        |  |  |  +--rw upper-port?   inet:port-number
>>>         |        |  |  |  +--rw operation?    operator
>>>         |        |  |  +--rw destination-port-range!
>>>         |        |  |  |  +--rw lower-port    inet:port-number
>>>         |        |  |  |  +--rw upper-port?   inet:port-number
>>>         |        |  |  |  +--rw operations?   operator
>>>         |        |  |  +--rw next-header?                uint8
>>>         |        |  |  +--rw destination-ipv6-network?   inet:ipv6-prefix
>>>         |        |  |  +--rw source-ipv6-network?        inet:ipv6-prefix
>>>         |        |  |  +--rw flow-label?                 inet:ipv6-flow-label
>>>
>>>
>>> The difference though is small and comes down to a preference. Select one
>>> feature statement and get one container with everything in it, or define
>>> multiple feature statements and assemble together the pieces to define the ACE
>>> entry.
>> Again, I think you mix up the features available vs the structure
>> of the data.
>>
>> This is the current list of features (which again, I want to
>> change but that's separate):
>> * l2-acl
>> * ipv4-acl
>> * ipv6-acl
>> * mixed-ipv4-acl
>> * mixed-ipv6-acl
>> * l2-l3-ipv4-ipv6-acl
>> * tcp-acl
>> * udp-acl
>> * icmp-acl
>> * any-acl
>>
>> As per your second example above we have an ipv4-acl container
>> under matches, i.e. /access-list/acl/aces/ace/matches/ipv4-acl.
>> It is only possible to define ipv4 matches if one of the
>> following features are present:
>> * ipv4-acl
>> * mixed-ipv4-acl
>> * l2-l3-ipv4-ipv6-acl
>>
>> Thus you write an if-feature statement to reflect that, like
>> this:
>>
>> if-feature "ipv4-acl mixed-ipv4-acl l2-l3-ipv4-ipv6-acl";
>>
>> So you see, the tight coupling you have between the data
>> structure and the if-features isn't necessary.
>>
>> I think the structure should first be established without
>> features and then features can be inserted where they make sense
>> to make part of the model optional. Starting with the list of
>> features and then designing the structure around them makes for a
>> much less natural data structure IMHO.
>>
>> Kind regards,
>>    Kristian.
> Mahesh Jethanandani
> mjethanandani@gmail.com
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